1. Field of the Invention
The present invention relates to a method of cleaning a processing chamber of a semiconductor processing apparatus, e.g., a CVD (Chemical Vapor Deposition) apparatus. Note that “semiconductor processing” means various processes performed to form semiconductor layers, insulating layers, conductive layers, and the like into predetermined patterns on a target substrate, such as a semiconductor wafer or LCD substrate, thereby fabricating a structure including a semiconductor device and lines, electrodes, and the like connected to the semiconductor device on the substrate.
2. Description of the Related Art
In the fabrication of a semiconductor device, various semiconductor processing apparatuses are used to perform processes, such as film formation, etching, oxidation, and diffusion, on a target substrate, e.g., a semiconductor wafer. As one type of such semiconductor processing apparatuses, a single-substrate heat-processing apparatus which processes wafers one by one is known. In a typical single-substrate heat-processing apparatus, a worktable (suscepter) for placing a wafer on it is disposed on the bottom of a processing chamber, and a shower head having a number of holes for supplying a process gas is disposed above the suscepter. An exhaust pipe for exhausting the processing chamber is connected to the processing chamber. A heater for heating a wafer is disposed below the suscepter.
As the material of the casing of the processing chamber, a corrosion-resistant material, such as anodized aluminum, stainless steel (SUS), or Ni, is used so that the material is not corroded by the process gas. As the material of the suscepter, a ceramic material having a high corrosion resistance is used.
In a CVD process for forming a thin film on the wafer surface, a process gas, such as SiH4, NH3, TEOS (tetraethylorthosilicate), Ta(OC2H5)5, is used in accordance with the composition of the thin film. In this CVD process, the process gas provides a film material on the wafer surface by thermal decomposition, and a thin film is deposited on the wafer surface by this film material.
In the CVD process, at the same time the thin film is formed on the wafer surface, a decomposition product of any of the above process gases adheres as a so-called by-product film to the surfaces of, e.g., the suscepter as a wafer support member and the casing walls of the processing chamber. This film attaching to internal portions of the processing chamber except for the wafer builds up as the CVD process is repeated. When the thickness of the by-product film increases, the film cracks and peels off by, e.g., a temperature change in the processing chamber. Consequently, the peeled by-product film turns into particles and is deposited on the wafer surface to cause device defects.
To prevent this particle contamination caused by the by-product film, cleaning is performed for the constituent members of the processing chamber, e.g., the casing walls and the suscepter (which either contains or does not contain a built-in heater) of the processing chamber. Representative conventional cleaning methods are: (a) the surface layers of the processing chamber constituent members are etched with an etchant, such as an aqueous HF solution, and then heating is performed in an inactive gas ambient; and (b) the by-product film is etched away by heating the interior of the processing chamber in a halogen-based cleaning gas ambient. Unfortunately, these cleaning methods have the following drawbacks.
Method (a) requires a long cleaning time because wet cleaning is the main process. Also, the method requires complicated operations, such as detachment, disassembly, attachment, and assembly of the constituent members. This reduces the productivity because, e.g., the operating efficiency of the semiconductor processing apparatus lowers.
Method (b) is performed by heating the interior of the processing chamber by filling the processing chamber with a halogen-based cleaning gas, such as ClF3, NF3, NCl3, HCl, Cl2, HF, F2, or CF4. The processing chamber, after the CVD process, contains water whose sources are, e.g., adsorption of water by cold walls, a hydroxyl group contained in the process gas, and water contained in the film itself. This residual water reacts with a halogen element contained in the cleaning gas to produce hydrogen halide. This hydrogen halide corrodes the metal of the casing of the processing chamber, and the produced metal halide scatters on the wafer to cause metal contamination. Even if no water exists in the processing chamber, a halogen element remains in the processing chamber and corrodes the constituent members of the processing chamber in subsequent processes. This results in an adverse effect, such as metal contamination of the wafer.
Methods of preventing this metal contamination are: (c) before a predetermined process, cleaning is performed by the same type of gas as a process gas used in the predetermined process (Jpn. Pat. Appln. KOKAI Publication No. 5-144802); and (d) the surface layers of the constituent members of the processing chamber are thermally oxidized to passivate impurities in these surface layers by oxidation, thereby reducing or suppressing diffusion of the impurities (Jpn. Pat. Appln. KOKAI Publication No. 11-135437). Unfortunately, these methods have the following drawbacks.
In method (c), etching is performed by the same type of gas as a process gas, but the process gas itself is not an optimal etchant. That is, all metal elements cannot be removed, so the cleaning effect is limited. In fact, according to Jpn. Pat. Appln. KOKAI Publication No. 5-144802, cleaning by the process gas is performed after the surface of an object is etched with a chemical, resulting in a complicated operation. Also, this method cannot remove a thickly adhered by-product film, so the method cannot eliminate the cause of particle contamination.
Method (d) forcedly oxidizes the surface layers of the processing chamber constituent members, i.e., passivates these surface layers, thereby suppressing diffusion of impurities. Accordingly, even when cleaning is performed by this method, metal elements themselves are not reduced in the processing chamber. That is, when this method is used, metal oxides build up in the processing chamber although cleaning is performed. This limits the number of times of cleaning which can be performed by repeating this method alone. Furthermore, this method cannot remove the by-product film itself either, so the method cannot eliminate the cause of particle contamination.
As described above, either of the conventional cleaning methods cannot well eliminate the cause of particle contamination and the cause of metal contamination. Therefore, when either cleaning method is used, the reliability of semiconductor device fabrication worsens, and this consequently lowers the productivity and increases the production cost. Especially because semiconductor devices are presently advancing in performance and integration degree, a more effective semiconductor processing apparatus cleaning technique is expected.